It is known that certain rubber compositions are very sensitive to the action of ozone. Vulcanized rubber compositions based on dienic elastomers are particularly sensitive.
When an article made with such a vulcanized elastomer composition is subjected to the action of prolonged static and dynamic stresses in the presence of ozone, some more or less marked cracks which can be seen on the surface of the article appear. These cracks are oriented perpendicularly to the direction of the stress, and their growth under the effect of said remaining stress may cause complete failure of the article.
In order to minimize these effects of ozone, antiozone compounds, which are designed to slow down the formation and propagation of the cracks under static and dynamic stressing conditions, are commonly incorporated into these articles and, particularly, into the sidewalls based on elastomers that are included in tires. Waxes are also commonly used to provide additional static protection by forming a protective coating on the surface of the sidewalls.
The association of antiozone compounds and waxes has proven to be effective for the minimization of cracks at the surface of the sidewalls.
Unfortunately, the most effective antiozone compounds also have a very high tendency to migrate through their polymeric substrate, which results in staining and coloring of the surfaces that are adjacent to said substrate. More precisely, yellowish or brown stains appear at the surface of the sidewalls. This phenomenon is called xe2x80x9ccolorationxe2x80x9d.
The Japanese Patent Document JP-A-5 194790 discloses, in a rubber composition for the sidewalls of a tire comprising at least one elastomer, the use of several specific polymeric surfactants of the polyoxyethylene ether type, in order to cope with the xe2x80x9ccolorationxe2x80x9d phenomenon. Those particular surfactants are characterized by a hydrophilic-lipophilic balance (HLB) which is comprised between 1 0.7 and 15.0, and they are made of polyoxyethylene nonylphenylether, polyoxyethylene stearylether, or polyoxyethylene oleylether.
The present invention relates to a tire including sidewalls which comprise a vulcanized rubber composition based on at least one elastomer. The invention is useful for the protection of a tire against the effects of migrations of antioxidants and antiozonants compounds incorporated in the sidewalls, which effects can be seen on the outer faces of the sidewalls.
A tire according to the invention includes sidewalls which comprise a rubber composition, wherein the rubber composition comprises between 0.5 phr and 10 phr (weight parts per hundred parts of rubber) of at least one polymer which comprises an oxy group having the formula xe2x80x94Oxe2x80x94 and, linked to the one side of the oxy group, at least one polyoxyalkylene block having the formula (CnH2nO)x,
where n is 2 or 3,
where x is an integer or decimal number from 2 through 15,
wherein the block is linked to an hydrogen atom which is located at the chain end of the polymer, such that the hydrogen atom forms an alcohol function with the terminal oxygen atom of the block, and
linked to the other side of the oxy group, an aliphatic moiety selected from the group consisting of:
a blend of aliphatic alkyl chains having an average number of carbon atoms from 10 through 14, and
an aliphatic alkyl chain having 13 carbon atoms.
The sidewalls of the tires of the present invention have an uniform black appearance which is durable and therefore significantly enhances the aesthetic appearance of the tires.
According to one embodiment of the invention, the aliphatic moiety is a blend of aliphatic alkyl chains having an average number of carbon atoms from 10 through 14.
In a preferred embodiment, the average number of carbon atoms is substantially equal to 14, and the at least one block consists of a sole polyoxyethylene block wherein x is equal to 4. Then, the hydrophilic-lipophilic balance (HLB) of said polymer is substantially equal to 9.1.
This embodiment wherein the average number of carbon chains is substantially equal to 14 not only provides a black color for the whole outer surface of the sidewalls, but also a glossy appearance for the surface which further enhances the sidewalls.
In another preferred embodiment, the average number of carbon atoms is substantially equal to 14, and the at least one block consists of: a polyoxypropylene block wherein x is equal to 5, and a polyoxyethylene block wherein x is equal to 4.
Then, the HLB of the polymer is substantially equal to 9.5.
Again in this particular embodiment, a glossy black color is obtained for the sidewalls.
In another preferred embodiment, the average number of carbon atoms is substantially equal to 12, and the at least one block consists of a sole polyoxyethylene block wherein x is equal to 7.
Then, the HLB of the polymer is substantially equal to 12.6.
Again in this particular embodiment, a glossy black color is obtained for the sidewalls.
In another preferred embodiment, the average number of carbon atoms is substantially equal to 14, and the at least one block consists of a sole polyoxyethylene block wherein x is equal to 2.
Then, the HLB of the polymer is substantially equal to 5.9.
Again in this particular embodiment, a glossy black color is obtained for the sidewalls.
In another preferred embodiment, the average number of carbon atoms is substantially equal to 10, and the at least one block consists of a sole polyoxyethylene block wherein x is equal to 2.5.
Then, the HLB of the polymer is substantially equal to 8.2.
Again in this particular embodiment, a glossy black color is obtained for the sidewalls.
According to another embodiment of the invention, the aliphatic moiety which is linked to said oxy group consists of a tridecyl group, and the at least one block consists of a sole polyoxyethylene block wherein number x is equal to 3.
Then, the HLB of said polymer is substantially equal to to 8.6.
The tires of the invention may be made using processes known to those of skill in the art. The polymers m a y be synthesized by standard organic chemistry methods or may be obtained commercially.